Fuel injectors which utilize engine lubricating oil as actuation fluid are sometimes subject to performance diminutions at cold start due to viscous oil flowing into an armature cavity defined by the injector body and a solenoid. During a cold start, the highly viscous cold oil can inhibit the movement of the armature. In turn, injector performance can be adversely affected by the slowing down and/or restricted movement of the armature. One method for dealing with this problem is taught in U.S. Pat. No. 5,375,576 to Ausman et al. and involved positioning an o-ring seal in the fuel injector to prevent viscous oil from flowing into the armature cavity. Additionally, the poppet valve and sleeve in these previous fuel injectors were machined to tight clearances to aid in prevention of viscous oil flow into the armature cavity. By preventing the flow of cold oil into the armature cavity, the performance problems associated with viscous oil surrounding the armature during cold start can be avoided. Although the sealing and clearance solutions of Ausman have worked well for years, geometrical and spatial constraints do not always allow for the implementation and use of these solutions. Thus, in some fuel injectors a different solution must be found to alleviate the problems associated with cold start.
The present invention is directed to overcoming one or more of the problems described above and to improving fuel injector performance at cold start.